1. Field of the Invention
The present invention is in the field of, for example, photocopiers, and more particularly for detecting the number of copy sheets remaining in a paper feeder which holds a stack of copy paper sheets therein and which is adapted to lift the stock to a specific position every time the height of the stack decreases by a predetermined amount.
2. Description of the Prior Art
Various forms of paper feeders for copying machines, printing machines, and the like have been generally known and accommodate a large number of copy sheets of paper that are arranged in stacks for copying and printing. Usually the stacks of copying paper are held within the photocopier or printing machine and are sequentially supplied to a processing station by an automatic feed mechanism. Copy paper feeders of this type are adapted to accommodate a larger number of sheets than detachable cassettes which have gained popularity in recent years. Thus the stacked paper feeders are usually more useful for high speed copying machines and those applications that require a continuous feed of a large number of sheets of copy paper.
Paper feeders that can accommodate a large stack of copy sheets have a drawback in that the stack is usually inaccessible or inconvenient to the user. It is frequently impossible to check the number of remaining copy sheets that are still in the machine and the machine will frequently automatically cease copying when the copy sheets decrease to a stack height of a predetermined amount.
The prior art has suggested paper feeders which would incorporate a mechanical index that would be movable with the decreasing amount of sheets or which would give a display of "Near Empty" to indicate that the stack has reduced to below a specific height. These proposed indexing or display methods, although capable of approximately showing the number of remaining copy sheets in the machine, fail to provide an accurate count. Another problem exists with a display system in that, after a period of time or when a different person uses the machine, generally the user is incapable of relying upon the display to provide even a rough approximation of the number of sheets that are still remaining in the machine. Consequently, the user may set the machine to reproduce a number of copies that are larger than the number of remaining copy sheets that are available. Finally, the use of a mechanical index to disclose the height of the stack has an inherent problem in that the actual number of copy sheets that may be positioned in any one stack arrangement can vary depending upon the thickness of the sheets, although the same height is indicated by the index.
The prior art is still looking for a convenient and economical apparatus that can be utilized in a photocopying environment to determine the actual number of copying sheets that are available to the user at any one time.